1. Field of the Invention
This invention relates to a method of preserving agricultural products which are used for animal feed after storage under anaerobic conditions.
2. Brief Description of Background Art
The use of silage additives has become a widely accepted practice throughout much of the agricultural world. In order to understand how silage additives react with silage, it may be helpful to first review the basic biochemical and microbiological changes that occur during the ensiling process. Immediately upon chopping of, for example, corn, aerobic respiration starts. During this early phase, soluble carbohydrates in the plant tissue are oxidized and converted to carbon dioxide and water. This process will continue until either the oxygen level is depleted or the water soluble carbohydrates are exhausted. Under ideal conditions, with adequate packing and sealing of the ensiled material, respiration lasts only a few hours. The growth of microorganisms during this period is limited to those that are tolerant to oxygen which includes aerobic bacteria, yeast and molds. These organisms are generally recognized as being negative to the system as they metabolize sugar to carbon dioxide, heat, and water.
Another important chemical change that occurs during this early phase is the breakdown of plant protein by plant proteases. Proteins are degraded to amino acids and further metabolized to ammonia and amines. It has been reported that up to 50% of the total proteins may be broken down during this process depending on the rate of pH decline in the silage.
Once anaerobic conditions are established, anaerobic bacteria proliferate. Enterobacteria and heterofermentative lactic acid bacteria are generally the first populations to become established. These organisms produce primarily acetic acid, ethanol, lactic acid, and carbon dioxide from the fermentation of glucose and fructose. Once the pH begins to decline, there is a marked increase in the homofermentative lactic acid bacteria population which produce primarily lactic acid. The rapid increase in lactic acid level results in the decline of the pH to around 4. At this point, the ensiled mass will generally remain stable throughout storage if undisturbed.
In summary, when the material is initially packed in an oxygen limiting structure such as a covered silo, the pH is reduced, the residual oxygen is utilized and the material is said to undergo a lactic acid fermentation. The material will remain stable and can be stored for many months in this condition.
When the silage is ready to be fed, the top cover is removed and the silo is opened for feeding. The material is then exposed to air and the process is no longer anaerobic. Microflora in the silage itself or airborne contaminants can begin to oxidize the acids present. This oxidation causes a loss in mass or dry matter of the feed and thus causes feeding losses. In addition, the resultant pH and temperature increases are objectionable to the animals and the feed will be refused by the animals after it has begun to heat. The incidence of aerobic instability observed in practice depends on the rate the ensiled material is removed from the silo and the length of time that the material has been ensiled before opening. If the silage is unloaded slowly then more time is allowed on the surface of the opened silage for deterioration to occur. Longer ensiling times produce generally more stable silage as the acid concentrations are higher and all microflora populations tend to decrease. In general the silage should be stable for at least five days after opening. This will allow for adequate time for the silage to be removed.
Recently it has become known that bacterial inoculants help preserve silage, including both grass silage and corn silage. For example, inoculation with lactic acid bacteria during the fermentation phase can be beneficial to the fermentation process, see for example U.S. Pat. No. 4,842,871 of Hill issued June 27, 1989, as well as the literature references cited therein. For high moisture corn stability, this increase is probably due to the inoculant enhancing the rate of anaerobic fermentation and pH decrease. This is beneficial because oxidative losses caused by aerobic pH sensitive microflora in the initial stages are thus avoided. In other silages such as whole corn plant, alfalfa, etc. the inoculant can also have beneficial effects on the digestibility of the silages by causes an increase in the availability of the fiber.
Currently there is not an inoculant available to effect stability in the second part of the process that occurs when the silo is opened to air. One reason for this lack of an effective inoculant is the antagonistic nature of anaerobic and aerobic preservatives. Each may interfere with performance of the other.
Accordingly, it is a primary objective of the present invention to develop a bacterial silage inoculant which is effective both during the initial anaerobic stages and also which will maintain effectiveness during the initial aerobic stages when a silo is opened to air.
Another objective of the present invention is to develop a silage inoculant which is effective in both stages, with the second stage inoculant also being an anaerobe and being one which does not in any way interfere with any initial anaerobic stage lactic acid producing bacteria inoculant which may be present.
Another objective of the present invention is to provide a silage inoculant which contains certain species of Propionibacteria which have been found to function effectively in the environment of lactic acid bacteria without either antagonizing the other. This results in effective silage preservative capability both during the initial anaerobic phase and because of the metabolic products of the Propionibacteria also during the subsequent aerobic phase.
The method and manner of accomplishing each of the objectives of the present invention as well as others will become apparent from the detailed description which follows hereinafter.